Previousattempts to develop a vaccine that would prevent disease associated with RSV have failed. In particular, a formalin treated whole virus vaccine, known as the Lot 100 Pfizer vaccine, not only failed to protect but also produced disease potentiation in young, immunized children. The causes for the lack of protective immunity and enhanced disease are not completely understood. Investigators in other laboratories have suggested an imbalance in the immune response; more specifically, a lack of fusion inhibiting antibody and little neutralizing antibody in the presence of high titers of RSV specific binding antibody. In order to gain additional insight into the antigenic structure of formalin treated RSV versus untreated virus we used a large panel of RSV specific neutralizing and non-neutralizing F and G monoclonal antibodies and compared reactivity of these antibodies in ELISAs. Preliminary data demonstrates that pretreatment with formalin will completely abolish reactivity for some neutralizing monoclonal antibodies. This is in contrast to the enhanced reactivity seen with non-neutralizing F and G monoclonal antibodies.